By the treaty of the 22d of February, 1819, between the United States and Spain, the Sabine was adopted as the line of boundary between the two powers. Up to that period no considerable colonization had been effected in Texas; but the territory between the Sabine and the Rio Grande being confirmed to Spain by the treaty, applications were made to that power for grants of land, and such grants or permissions of settlement were in fact made by the Spanish authorities in favor of citizens of the United States proposing to emigrate to Texas in numerous families before the declaration of independence by Mexico.
The Texas which was ceded to Spain by the Florida treaty of 1819 embraced all the country now claimed by the State of Texas between the Nueces and the Rio Grande. The Republic of Texas always claimed this river as her western boundary, and in her treaty made with Santa Anna in May, 1836, he recognized it as such. By the constitution which Texas adopted in March, 1836, senatorial and representative districts were organized extending west of the Nueces. The Congress of Texas on the 19th of December, 1836, passed "An act to define the boundaries of the Republic of Texas," in which they declared the Rio Grande from its mouth to its source to be their boundary, and by the said act they extended their "civil and political jurisdiction" over the country up to that boundary. During a period of more than nine years which intervened between the adoption of her constitution and her annexation as one of the States of our Union Texas asserted and exercised many acts of sovereignty and jurisdiction over the territory and inhabitants west of the Nueces. She organized and defined the limits of counties extending to the Rio Grande; she established courts of justice and extended her judicial system over the territory; she established a custom-house and collected duties, and also post-offices and post-roads, in it; she established a land office and issued numerous grants for land within its limits; a senator and a representative residing in it were elected to the Congress of the Republic and served as such before the act of annexation took place. In both the Congress and convention of Texas which gave their assent to the terms of annexation to the United States proposed by our Congress were representatives residing west of the Nueces, who took part in the act of annexation itself. This was the Texas which by the act of our Congress of the 29th of December, 1845, was admitted as one of the States of our Union. That the Congress of the United States understood the State of Texas which they admitted into the Union to extend beyond the Nueces is apparent from the fact that on the 31st of December, 1845, only two days after the act of admission, they passed a law "to establish a collection district in the State of Texas," by which they created a port of delivery at Corpus Christi, situated west of the Nueces, and being the same point at which the Texas custom-house under the laws of that Republic had been located, and directed that a surveyor to collect the revenue should be appointed for that port by the President, by and with the advice and consent of the Senate. A surveyor was accordingly nominated, and confirmed by the Senate, and has been ever since in the performance of his duties. All these acts of the Republic of Texas and of our Congress preceded the orders for the advance of our Army to the east bank of the Rio Grande. Subsequently Congress passed an act "establishing certain post routes" extending west of the Nueces. The country west of that river now constitutes a part of one of the Congressional districts of Texas and is represented in the House of Representatives. The Senators from that State were chosen by a legislature in which the country west of that river was represented. In view of all these facts it is difficult to conceive upon what ground it can be maintained that in occupying the country west of the Nueces with our Army, with a view solely to its security and defense, we invaded the territory of Mexico. But it would have been still more difficult to justify the Executive, whose duty it is to see that the laws be faithfully executed, if in the face of all these proceedings, both of the Congress of Texas and of the United States, he had assumed the responsibility of yielding up the territory west of the Nueces to Mexico or of refusing to protect and defend this territory and its inhabitants, including Corpus Christi as well as the remainder of Texas, against the threatened Mexican invasion.